Treatment with riboflavin (RF) followed by ultraviolet A (UVA, 370 nm) illumination results in cornea stiffening and sclera stiffening presumably because of collagen crosslinking (CXL). This has increasingly been used for halting the progression of keratoconus and post refractive laser surgery corneal ectasia (Wollensak et al., 2003(a); Hafezi et al., 2007; Raiskup-Wolf et al., 2008). However, there are several drawbacks to this treatment: (1) The prolonged time of RF treatment (30 min); (2) The prolonged eye exposure to UVA irradiation (30 min), and finally (3) Toxicity to keratocytes (Wollensak et al., 2004(a); Wollensak et al., 2004(b); Wollensak, 2010(a)) and corneal endothelial cells (Wollensak et al., 2003(c); Spoerl et al. 2007), making treatment of corneas thinner than 400 microns problematic (Hafezi et al., 2009; Wollensak, 2010(b)). Hence, there is a need for a safer treatment that can stiffen the cornea with a lesser risk to the patient (Avila and Navia, 2010; WO/2008/052081). One possibility is to use photosensitizers that inflict cornea stiffening upon illumination at the near infra red (NIR) using bacteriochlorophyll derivatives as photosensitizers.
Myopia, also termed nearsightedness is a refractive defect of the eye in which collimated light produces the image focus in front of the retina when accommodation is relaxed. The global prevalence of myopia has been estimated from 800 million to 2.3 billion. In some countries, such as China, India and Malaysia, up to 41% of the adult population is myopic to −1 dpt and about 80% to −0.5 dpt. Myopia has been related with stretching of the collagenous sclera. Elongation of the globe occurs in the posterior segment of the globe and involves the sclera. Such globe elongation causes myopic progression in predisposed myopic children and adolescents. It usually slows down and stops during the third decade of life, when maturation of body tissues occurs with natural stiffening. This stiffening is related to glycation mediated cross linking.
At present, there is no effective treatment to stop myopic progression and reduce visual loss caused by degenerative myopia. Surgical solutions to arrest myopic progression by applying reinforcement belts around the eye, and suturing them to the sclera, were reported. These surgical solutions were controversial and technically challenging, and did not gain popularity. The critical age of intervention is during childhood or early adolescence. Thus, a simpler approach to stiffen the sclera should be applied.
Since progression of myopia is associated with elongation of the posterior segment of the eye and subsequent stretching of the sclera and chorioretinal tissues, stiffening of the sclera by collagen crosslinking, is expected to retard/stop the progression of the disease and related disorders such as macular stretching and atrophy or bleeding and visual loss. Wollensak and Spoerl reported the use of RF/UVA treatment to achieve such crosslinking and strengthening in human and porcine sclera in vitro. The crosslinking stiffening was demonstrated in vivo on rabbits, and was shown to last several months. This treatment can be applied to arrest myopic progression.
However, such treatment is subjected to the UVA risks which might be hazardous. In addition, the tissue penetration of UV radiation is limited. Illumination of the sclera with UV requires external approach and necessitates surgical exposure. There is therefore, a need for alternative photosensitizers that can induce collagen crosslinking with a safer and better penetrating wavelength at the red or near infrared (NIR).
A non hazardous light with deeper tissue penetration, like NIR in bacteriochlorophyll (BChl)-based PDT has been shown to provide efficient and safe anti-cancer treatments in oncology and age related macular degeneration in the eye (AMD) (U.S. Pat. No. 7,947,672, WO 2005/120573).
Application of novel water soluble chlorophyll (Chl) and bacteriochlorophyll (BChl) derivatives as sensitizers in PDT has been reported by the present inventors in recent years (U.S. Pat. No. 7,947,672; WO 2005/120573; Ashur et al. 2009; Mazor et al. 2005; Brandis et al., 2005) and by others (Moore et al., 2009; Bourges et al., 2006; Berdugo et al. 2008). Upon NIR illumination these water soluble derivatives generate O2− and .OH radicals (Ashur et al. 2009; Mazor et al. 2005; Brandis et al., 2005; Vakrat-Haglili et al., 2005) and have been used so far in vascular-targeted photodynamic therapy (VTP) of cancers in preclinical (Mazor et al. 2005) and advanced clinical trials of prostate cancer therapy (currently in Phase III) (Trachtenberg J et al. 2007; Lepor H. 2008; Moore et al., 2009), following i.v. administration to the treated patients. The effective generation of oxygen radicals as precursors of protein crosslinking (Liu et al., 2004), and the clinical experience established with water soluble Bchls and Chls derivatives, makes these sensitizers potential candidates for application in therapy that is mediated by collagen crosslinking, particularly corneal and scleral stiffening upon NIR illumination after topical application.